"The longitude problem" was the thorniest scientific dilemma of the 18th century; with no way to measure east-west distance on the ocean, sailors throughout time had been lost at sea as soon as they were out of sight of land. In 1714 the British Parliament offered the staggering sum of £20,000 (approximately $12 million today) to anyone who could accurately measure longitude. Clockmaker John Harrison imagined a simple mechanical solution—a clock that would keep precise time at sea, something no clock had ever been able to do on land—and embarked on a 40-year obsession with building the first true chronometer. Winning numerous awards, including the 1997 British Book Awards Book of the Year, and earning its author a fellowship in the American Geographical Society, Longitude is "a wonderful story, wonderfully told.... Only someone with Dava Sobel's unusual background in both astronomy and psychology could have written it."—Diane Ackerman